SUMMARYAircraft observations of cloud and precipitation particles just below the tops of Florida cumuli at temperatures near -4 and -9°C show that fresh, vigorously growing towers (updraughts of order IOms-I) tend to contain low concentrations ( < O l I-') of graupel, whereas older towers with lower updraught speeds contain much higher concentrations (> 101-I). The ice phase, mostly as graupel, was often found to appear within a period of five minutes. Cloud drops of diameter > 25 pm were always found to be present in concentrations of 10 to lOOcm-' between -4 and -6°C. a condition, according to criteria established by laboratory studies, necessary for secondary ice crystal production by the riming of graupel particles. Vapourgrown columns in concentrations as high as 50 I-' were sometimes observed at the colder level. an observation consistent with the concept of a copious production zone below. Supercooled raindrops in concentrations > 1 I-' occur in many regions of the clouds, often concurrently with graupel and crystalline ice. It is shown by means of a simple analytical model that aerodynamic capture of secondary ice particles by the supercooled raindrops and the subsequent transformation of the raindrops to new splinter-producing graupel may be the main mechanism responsible for the rapid increase in observed graupel concentrations. The coalescence processes are therefore seen to be instrumental in the evolution of the ice phase. This process is favoured in lower updraught regions where the particles can be retained in the -4 to -6°C production zone long enough (" 100s) for the entire feedback process of splinter production, capture, drop freezing and renewed splinter production to take place. 1, INTRODUCTIONAlthough the evolution of the ice phase has been thought to be the dominating influence on precipitation formation in most clouds extending significantly above the freezing level, evidence is mounting that the effective glaciation of such clouds is itself dependent upon the prior evolution of the liquid phase by the coalescence precipitation mechanism. Aircraft observations (Koenig 1963) have shown that large precipitation-sized supercooled drops were associated with the rapid evolution of the ice phase in Missouri summer cumuli having top temperatures mostly above -10°C. Mossop et a/. (1968, 1970, 1972) have provided additional evidence for rapid and prolific ice formation in maritime clouds developing over Australia, the observed concentrations of ice particles exceeding an extrapolation of detected concentrations of ice nuclei by factors > lo4. They concluded that the riming process and the presence of large drops are of prime importance for rapid glaciation.More recently, the laboratory studies of Hallett and Mossop (1974) and Mossop and Hallett (1974) showed that the production of secondary ice particles during the growth of graupel between -4 and -6°C required the presence of a cloud drop spectrum with a tail extending beyond approximately 25 pm diameter, with one ice particle produced duri...
Complexes of the potentially tetradentate ligand isonitrosoacetylacetone dithiosemicarbazone (inbtH2) of formulae [Ti(inbtH2)C12]C12, [M(inbt)], where M = VIVO, Mn II, Ni n or Zn n, [M(inbtH2)X2] , where M = Co II and X = C1, or M = Ni n and X = C1, Br or I, and [M(inbtH2)C12]C1, where M = Cr lu or Fe m, have been prepared and characterized by physico-chemical and spectroscopic methods.In all the compounds the metal is coordinated by the thiocarbonyl sulphur and imine nitrogen, as revealed by i.r. studies. The n.m.r, spectra of the complexes ofNi n and Zn ~ confirm coordination through nitrogen. Possible structures for the complexes are proposed. The M6ssbauer spectrum of the Fe II~ complex is discussed.
The results of analysis of the data collected on the concentrations of the ice-forming and other forms of nuclei in a few places in India (Delhi, Calcutta, Bombay, Lonavla and Poona) have been presented.The ice-forming nuclei have varied generally inversely with the chloride nuclei at Delhi, Bombay and Poona.The ice-forming and hygroscopic nuclei have shown negative correlation at Delhi.The ice-forming and non-hygroscopic nuclei have varied on parallel lines at Poona.The relatively large value of the ice-forming nuclei noticed at Delhi as compared to that at Calcutta has been seen reflected in the high value of the non-hygroscopic nuclei observed in that region.The observations have suggested that the main source for the ice-forming nuclei in the regions measured is the land.The possibility of the continental dust being responsible for the observed ice nuclei counts in the maritime air has been pointed out.
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